Paint can be removed from the surfaces of masonry structures in a variety of ways. Thus, brushing and scrubbing manually, steam cleaning, burning, chemical cleaning and sandblasting have all been used over the years with varying degrees of success. While chemical cleaning and sandblasting are consistently the most effective methods, they are also by far the most destructive, particularly as applied to brick work. The bricks of commerce are kiln-fired, pressed clay products which, in their mint condition on emerging from the kiln, have a bisque or enamel coating covering a porous pulp or interior structure comprising the main mass of the body of the brick. In the chemical cleaning operation, paint is removed but the chemicals etch, as well as dissolve, the surface of the brick exposing the pulp-like, porous interior structure. Further, the chemicals form silica salts with the brick structure which are absorbed by the pulp of the brick only to bleed outside on the surface of the brick after the job has been finished for some time. The brick is also weakened structurally by such chemical action so that the physical integrity of the structure as well as its aesthetic character is somewhat diminished. Sandblasting, on the other hand, results in destruction of the exterior surface or bisque which is completely eroded away, leaving the weaker pulp of the brick mass exposed. Again, the structure of the brick is weakened and the brick is exposed to rapid weathering action by the elements and corrosive air pollution components.
As a general proposition, the alternative to using these paint removing processes is to leave the paint in place on the exterior surface of a brick wall of a building, but experience has shown that this is not practicable for other reasons. Thus, even though the paint is initially attractive in appearance, it promotes breakdown and is otherwise detrimental, particularly in those buildings where there is no wall insulation or vapor barrier, as is generally the case in historical buildings. This is because the paint coating acts as a barrier to the dissipation of water vapor that develops inside buildings and this moisture is trapped within the pores of the brick so that during freeze/thaw cycles it causes spalling of the brick exterior surfaces. In addition, by blocking dissipation of moisture, the paint coating results in increased humidity within the structure causing decay of lumber and other biodegradable components in the walls, peeling of the paint on the inside surface and excessive condensation and consequent physical discomfort of building occupants.